1. Field of the Invention
The present invention relates to a pipe joint structure for connecting a fluid carrying pipe to any of the fluid handling devices such as a variety of valves including stop valves and the like, filters, pumps, flowmeters, tanks and the like.
A pipe joint structure for any of the fluid handling devices mentioned above is strongly required to have such sealing properties as to prevent a fluid flowing inside of a fluid carrying pipe from leaking to the outside thereof even though the fluid temperature undergoes a change. In particular, when such a pipe joint is used for connection of a pipe in a semiconductor manufacturing apparatus or the like in which a medical liquid such as a strong acid or alkali liquid flows, the leakage of such a liquid to the outside, if any, may cause a serious accident. Thus, such a pipe joint is required to present highly reliable sealing properties. Further, the pipe for chemicals in the semiconductor manufacturing apparatus mentioned above is required to have resistance to chemicals, resistance to heat and purity maintaining properties. Accordingly, such a pipe is made of fluoroplastic typically represented by PFA ( a tetrafluoroethylene-perfluoroalkylvinylether copolymer). As compared with a metallic pipe, such a pipe made of fluoroplastic is liable to present a creep phenomenon particularly when heat is applied thereto. Accordingly, when a pipe joint is used for connection of a fluoroplastic pipe used for chemicals in a semiconductor manufacturing apparatus or the like, the pipe joint is required to have such sealing properties as to sufficiently deal with the creep phenomenon.
2. Discussion of the Prior Art
As a pipe joint structure suitable for connection of a pipe for chemicals in the semiconductor manufacturing apparatus as mentioned above, has already been proposed as a resin pipe joint having the arrangement shown in Japanese Utility Model Application No. 1-69378 (Japanese Utility Model Laid-Open Publication No. 2-117494). This resin pipe joint is arranged as shown in FIG. 4. More specifically, a fluid handling device body 30 such as a stop valve or the like is made of fluoroplastic excellent in resistance to chemicals and resistance to heat, such as PFA (a tetrafluoroethylene-perfluoroalkylvinylether copolymer) or PTFE (polytetrafluoroethylene), and a fluid passage 30A inside of the fluid handling device body 30 is provided at an end thereof with a tapering female screw portion 31 for connection. A joint body 33 is provided at one end thereof with a male screw portion 32 to be threadedly connected to the female screw portion 31, and at the other end thereof with a receiving port 37 into which is inserted a one-end pushing portion 36 of a fluid carrying pipe 35 made of PFA ( a tetrafluoroethylene-perfluoroalkylvinylether copolymer). Likewise the fluid handling device body 30, the joint body 33 is made of fluoroplastic excellent in resistance to chemicals and resistance to heat such as PFA (a tetrafluoroethylene-perfluoroalkylvinylether copolymer), PTFE (polytetrafluoroethylene). The joint body 33 is connected to the fluid handling device body 30 through the female and male screw portions 31, 32. An inner ring 34 serving as a sealing ring is pressingly inserted into the one-end pushing portion 36 of the fluid carrying pipe 35 to increase the same in diameter. A pushing ring 40 has a female screw portion 39 to be threadedly connected to a male screw portion 38 formed on the outer periphery of the joint body 33. Primary and secondary sealing portions 41, 42 are respectively formed at the inner part and inlet part of the receiving port 37, as inclined in the direction of the axis thereof. Sealing portions 43, 44 are respectively formed at the inner- and outer-end portions of the inner ring 34 such that these sealing portions 43, 44 respectively correspond to the primary and secondary sealing portion 41, 42. When the one-end pushing portion 36 is inserted into the receiving port 37 of the joint body 33, and the pushing ring 40 is threadedly moved, the joint body 33 is connected to the fluid carrying pipe 35 with a sealing force applied between the primary sealing portion 41 and the inner-end sealing portion 43, and between the secondary sealing portion 42 and the outer-end sealing portion 44.
According to the resin pipe joint having the arrangement shown in FIG. 4, the threaded movement of the pushing ring 40 can produce a strong sealing force between the sealing portions 41, 42 formed at the receiving port 37 of the joint body 33 and the sealing portions 43, 44 formed at the inner ring 34 pressingly inserted into the one-end pushing portion 36 of the fluid carrying pipe 35. Accordingly, this pipe joint restrains stress relaxation due to temperature variations, thus assuring excellent sealing properties between the joint body 33 and the fluid carrying pipe 35 in spite of variations of the fluid temperature. Further, the use of the inner ring 34 advantageously maintains the fluid carrying pipe 35 such that the fluid carrying pipe 35 is prevented from coming off from the joint body 33.
In the pipe joint having the arrangement mentioned above, however, the fluid handling device body 30 and the joint body 33 are separately formed and connected to each other through the female and male screw portions 31, 32. It is therefore difficult to prevent the fluid from leaking through the screw connection portions. In particular, when the pipe joint is used for connection of a pipe for chemicals in the semiconductor manufacturing apparatus or the like mentioned above, a chemical fluid such as a strong acid or alkali fluid flowing in the fluid carrying pipe 35 may leak from the screw connection portions, thus causing a serious accident. Further, there is used a pipe made of fluoroplastic excellent in resistance to chemicals, resistance to heat and purity maintaining properties, such as PFA (a tetrafluoroethylene-perfluoroalkylvinylether copolymer) or the like. Accordingly, as compared with the case where a metallic pipe is used, the fluid leakage through the screw connection portions is great and is liable to be further increased due to a creep phenomenon in particular when heat is applied.
The pipe joint having the arrangement above-mentioned has, at the screw connection portions thereof, a step portion A the diameter of which is greater than that of the fluid passage 30A. This step portion A forms a fluid staying portion. Accordingly, the purity of the fluid is liable to undergo a change when the fluid passes through this portion A. Thus, this pipe joint is not suitable for a pipe joint for a fluid device using a fluid of which high purity is required, such as a chemical fluid flowing in a pipe in a semiconductor manufacturing apparatus or the like as mentioned earlier. That is, such a pipe joint is restricted in use to a narrow range of applications.